# 24v wiring

Registered Users Posts: 10
Hi there
Great Forum, really helpful
I'm new to this forum, and new to solar power, I am hoping to get some advice on how to wire my solar set up.

I live on a boat in the uk, my set up is,,,

panels: 235 watt @ 38 amps, x4 total 960 watts
Batteries: 6v yuasa endurance 100 ah, sealed lead acid x 28
Controller: morning star 45 amp mppt
Inverter, currently have 12v but trying to decide weather to replace with 24v or 48v?

I'm confused as to how to wire the batteries for 24v? And would appreciate if someone could help me out with a diagram?

Oz

• Banned Posts: 17,615 ✭✭
Re: 24v wiring

You have twenty-eight 6 Volt batteries?
First let me say that wired as fourteen parallel strings of two in series for 12 Volts is a nightmare that almost certainly is not working optimally. The chances of the current being equal between all fourteen strings is about nil.

As for switching up to 24 Volt ... To make the Voltage you need strings of four. Four into twenty-eight is seven, so you'd have seven parallel strings of four in series. This is not a fantastic improvement over fourteen parallel strings.

Are you sure you need this much stored power? Right now you'd have 1400 Amp hours @ 12 Volts (700 Amp hours @ 24 Volts) or about 8.4 kW hours. That's quite a lot.

Your 960 Watts of panel would max out a 60 Amp MPPT controller, and that would be a peak charge rate of only 4% - not even the minimum recommended for most batteries, never mind after load loss.

I'd suggest you adjust your system o suit your 960 Watt array: for a 24 Volt system your 45 Amp MPPT controller would work. Batteries should be reduced to 300-ish Amp hours @ 24 Volts, or three parallel strings of four. This would be 3.6 kW hours stored capacity, and should be limited to 25% DOD or 1.8 kW hours daily. The 960 Watts of panel should be able to supply that on a good day.
• Solar Expert Posts: 3,009 ✭✭✭✭
Re: 24v wiring

Welcome to the forum "Ozparker"!

Couple of things - - first, your panels - - "235 watts @ 38 amps" - - I'm assuming you meant to say 235 watts @ 38 volts.
Most important is your batteries - - - Twenty eight batteries of 6 volts each. That many batteries are going to be trouble.
To get 24 volts, connect 4 of these 6 volt batteries in series. Then id you intend to use all of them, which I assume you are, you'll have to make 7 identical strings of 4 batteries, then connect the 7 strings in parallel. That's where the trouble will start. It will be virtually impossible to balance out the charging and discharging of all those strings so that all the batteries are charged and discharged equally, together, all the time. And this will create real problems for your batteries. In fact, 3 strings are the max recommended, because of this problem.
I'll leave this for thought and I'm sure others will chime in.
Thanks for joining the forum, and I hope you will gain from all the help available here.
Wayne
EDIT: As usual Cariboocoot is right on the job and faster than I am, so I didn't get to see his post until after mine went up.
• Solar Expert Posts: 295 ✭✭✭
Re: 24v wiring
You have twenty-eight 6 Volt batteries?
First let me say that wired as fourteen parallel strings of two in series for 12 Volts is a nightmare that almost certainly is not working optimally. The chances of the current being equal between all fourteen strings is about nil.

As for switching up to 24 Volt ... To make the Voltage you need strings of four. Four into twenty-eight is seven, so you'd have seven parallel strings of four in series. This is not a fantastic improvement over fourteen parallel strings.

Are you sure you need this much stored power? Right now you'd have 1400 Amp hours @ 12 Volts (700 Amp hours @ 24 Volts) or about 8.4 kW hours. That's quite a lot.

Your 960 Watts of panel would max out a 60 Amp MPPT controller, and that would be a peak charge rate of only 4% - not even the minimum recommended for most batteries, never mind after load loss.

I'd suggest you adjust your system o suit your 960 Watt array: for a 24 Volt system your 45 Amp MPPT controller would work. Batteries should be reduced to 300-ish Amp hours @ 24 Volts, or three parallel strings of four. This would be 3.6 kW hours stored capacity, and should be limited to 25% DOD or 1.8 kW hours daily. The 960 Watts of panel should be able to supply that on a good day.

If he is thinking of switching to 24v or 48v would seem 48v would be the winner. It would give the tristar some more room.

That would bring it down to 3 strings of 8 batteries in parallel. this situation would leave 4 batteries unused, but at 3 strings should result in much more equal charging. Although it is a bit much on batteries I could see a weekly usage of generator being used to stir the electrolyte a bit IF needed.

Matthew
• Banned Posts: 17,615 ✭✭
Re: 24v wiring
animatt wrote: »
If he is thinking of switching to 24v or 48v would seem 48v would be the winner. It would give the tristar some more room.

That would bring it down to 3 strings of 8 batteries in parallel. this situation would leave 4 batteries unused, but at 3 strings should result in much more equal charging. Although it is a bit much on batteries I could see a weekly usage of generator being used to stir the electrolyte a bit IF needed.

Matthew

Nope. Here's why:

The four panels would have to all be in series to produce sufficient Vmp for a 48 Volt system and use all the panels. At that point the Voc of the four would exceed the Morningstar's input maximum, even without cold temperature increase.

As I said the amount of battery capacity he has now is pretty high for the size of the array.

48 Volt systems are not always the wonderful solution some people think them to be. The circuit protection/disconnects needed to handle the higher Voltage are often hard to find or more expensive than what will work @ 24 Volts.

All things considered the best solution for him is to go up to 24 Volts and reduce the amount of battery he has, if that will fit with his stored power requirements. If he really does need all that capacity he would have to get more panel, or be prepared to run the generator quite a lot.
• Solar Expert Posts: 1,925 ✭✭
Re: 24v wiring
The four panels would have to all be in series to produce sufficient Vmp for a 48 Volt system and use all the panels. At that point the Voc of the four would exceed the Morningstar's input maximum, even without cold temperature increase.

As I said the amount of battery capacity he has now is pretty high for the size of the array.

Perhaps adding 2 more panels could solve both problems - he could go with 48 volts by doing 2 strings of 3 panels each, and more panels would be more adequate for the size of the bank.
• Banned Posts: 17,615 ✭✭
Re: 24v wiring
NorthGuy wrote: »
Perhaps adding 2 more panels could solve both problems - he could go with 48 volts by doing 2 strings of 3 panels each, and more panels would be more adequate for the size of the bank.

Which is why it is necessary to know what the power requirements actually are.
• Registered Users Posts: 10
Re: 24v wiring

Sorry I did mean 38v panels, not 38 amp.

I forgot to mention that I also have a 28 kw generator on board, but uses a lot of diesel so Only run it maybe 10 hrs per week.

I like the idea of 48v so I can add more panels later without upgrading the 45 amp controller.
I have room for 2 more 235 watt panels on my cabin roof.
I'm pretty much spent out at the moment, so I have to work with what I have for now.
Also Im happy not to use all of my batteries.

I also like the idea of 24v system as I can buy a good 24v inverter (sterling) at a reasonable price, but with 48v I've either got to spend a lot on a different brand (sterling don't make them) or go for a cheaper Chinese brand, which makes me nervous
Very confusing so I really appreciate all your advice
Oz

Ps, my main worry is the longevity of my battery bank, as this is the most expensive part of the system
• Registered Users Posts: 10
Re: 24v wiring

As for power usage,
240 v:

lighting 60 watts,
2 laptops,
TV
Hifi

12v/24v

mains pressure water pump x1
Shower waste pump

I'm going to add,
12/24v fridge,12v heating pump,

I have separate battery system for ships radio and depth finder etc
• Banned Posts: 17,615 ✭✭
Re: 24v wiring
Ozparker wrote: »
As for power usage,
240 v:

lighting 60 watts,
2 laptops,
TV
Hifi

12v/24v

mains pressure water pump x1
Shower waste pump

I'm going to add,
12/24v fridge,12v heating pump,

I have separate battery system for ships radio and depth finder etc

This information says what you use, not Watt you use.

You have to actually measure the power consumption of each device during typical usage to get a realistic Watt hour consumption. And the information supplied by the manufacturer isn't going to help much as those tags that give Amps @ Volts are usually always inaccurate. I'm sure there's such a thing as a Kill-A-Watt Europe (or its equivalent): get yourself one and save a lot of headaches in trying to figure it out otherwise.

For the DC devices you will either have to measure the current with a clamp-on DC meter (may not be easy to find over there) or interrupt the wiring and use a DMM (if it can handle the potential) or go for the shunt-type current meter (which you may want to keep an eye on things while in use anyway).

Right now unless you are checking the SG on the batteries and firing up the gen as needed your batteries are in danger of shortened lifespan due to insufficient charging as that is a pretty small array for that much battery.
• Super Moderators, Administrators Posts: 30,485 admin
Re: 24v wiring

It all comes down to your loads--In general, a balanced off grid system design would have about 2 days of battery storage and 50% maximum discharge--Or about 4x your daily battery loads.

A wild card (for me) is the 12 volt heating pump... Is that a simple water circulation pump and a "boiler" or a refrigeration "heat pump" (i.e., reversible air conditioner--In the US we call those a "Heat Pump"). If you have A/C and/or Heat Pump, that can be a whole lot of energy usage.

What you listed is not much energy usage... Maybe something like 3.3 kWH per day (wild guess). A 24 volt battery bank would be:
• 3,300 Watt*Hours * 1/0.85 inverter efficiency * 2 days of storage * 1/0.50 max discharge * 1/24 volt battery bank = 647 Amp*Hour @ 24 volt battery bank

So, your present battery bank is:
• 6 volts * 100 AH * 28 Batteries * 1/7 parallel strings = 700 AH @ 24 volts (with 4x 6 volt batteries in series x 7 strings).

So--Roughly, your present battery bank is about the right size--But your choice of batteries should be different (in my humble opinion). For example, at a minimum, use 6 volt @ 220 AH batteries. 4 batteries in series in 3 parallel strings would give you ~660 Amp*Hour @ 24 volts. Even larger batteries to get down to one or two parallel strings would be better.

You can go with even larger batteries--Such as Fork Lift -- But those batteries are on the order of 1/2 a ton (~600 kg). I guess that you will be moving the batteries around by hand, so you need to keep the batteries small enough for one or two people to move around. You could build a single string of 4 series (4 volt battery @ 683 AH each) 123 kg cells.

Charging wise from solar, we do two calculations--One sizing the panels for the battery bank, and second based on how much power you use and how sunny your area is... For example based on 5% to 13% rule of thumb charging:
• 660 AH * 29 volt charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,243 Watt array minimum
• 660 AH * 29 volt charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,486 Watt array nominal
• 660 AH * 29 volt charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,231 Watt array "cost effective maximum"

And based on hours of sun per day--In much of of the US, we can get 4 hours or more of "full noon time sun per day" for 9+ months of the year... Using PV Watts and London UK, fixed array tilted to latitude:
```Month    Solar Radiation (kWh/m2/day)
1      1.45
2      1.90
3      2.55
4      3.99
5      4.60
6      4.38
7      4.63
8      4.52
9      3.56
10      2.64
11      1.61
12      0.97
Year      3.07
```

2.55 hours of sun per day for 8 months a year:
• 3,300 Watt*Hour per day * 1/0.52 system eff * 1/2.55 hours of sun per day = 2,489 Watt array "break even" February

You have to pick the size of array based on how much room you have, and how much you can justify.

Regarding the genset--That is a very large generator for this size battery bank/set of loads... For the battery bank, a good sized rate of charge would be 5-13% (same as solar), but we can pick two numbers: 10% for "gentle" charging (most efficient both for battery life and fuel usage on genset) and 20% (25% maximum recommended) for reducing generator run-time (smoke and noise):
• 660 AH * 29 volts charging * 1/0.80 charger eff * 1/0.67 Power Factor * 0.10 rate of charge = 3,571 VA AC generator load "nominal"
• 660 AH * 29 volts charging * 1/0.80 charger eff * 1/0.67 Power Factor * 0.20 rate of charge = 7,142 VA AC generator load "bit over-sized battery charger" (watch battery bank temperature during charging)

For diesel gensets, generally you would want to run that at 40-60% minimum load for generator life (prevent wet stacking, carbon build up, cylinder wall glazing, etc.).

Of course, my calculations are all based on a guess of 3.3 kWH per day or, roughly:
• 3,300 WH * 0.85 inverter eff * 1/12 volt battery bank = 234 AH @ 12 volts per day

If your only loads are for the battery bank, you can use a much smaller genset and save a lot of fuel costs (probably 1/2 to 1/4 the fuel usage over your 48 kW genset)--Unless you use the genset for other loads (cooking, ship's loads, etc.).

Anyway--A quick back of the envelope calculation.

Can you give us a better estimate of power usage? 3.3 kWH per day is what I use for a small, energy efficient, off grid home with a full size (energy efficient) refrigerator, lights, laptop computer/TV/Cell Charger, water pump, washing machine type loads... Energy usage is a highly personal set of choices... What works for one person may not for another.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 295 ✭✭✭
Re: 24v wiring
Ozparker wrote: »

I also like the idea of 24v system as I can buy a good 24v inverter (sterling) at a reasonable price, but with 48v I've either got to spend a lot on a different brand (sterling don't make them) or go for a cheaper Chinese brand, which makes me nervous
Very confusing so I really appreciate all your advice
Oz

Ps, my main worry is the longevity of my battery bank, as this is the most expensive part of the system

I have looked at inverters before and the sterling inverters i have seen looked like LOW frequency inverters(big transformers/large surge). very similiar to those cheap chinese inverters it may even be made there. they do seem to have okay reviews. But it maybe the type of person using it has different expectations that an offgrid type user.

If you are talking about what I am thinking about I would look into idle power consumption. What the inverter takes to power itself is enormous amounts of juice.(I have a chinese built one). I bought mine knowing the situation. It is just a backup inverter for me to run some large loads. When you have a large load running of over 2000w an extra 65watts on self consumption is not a huge deal. But if you are only running a few leds and are using only 50watts of energy that 65watt self consumption is massive.

Just some thoughts.
matthew
• Solar Expert Posts: 295 ✭✭✭
Re: 24v wiring

i looked into sterling a bit more and there seem to be high frequency inverters as well. They should have lower power draws, but it is sometime to look at. Sterling seems more in Uk and Australian markets. I would assume by your user name your in Australia. Maybe someone else can recommend a decent inverter that is easily accesible to your location.
Matthew
• Registered Users Posts: 10
Re: 24v wiring
animatt wrote: »
i looked into sterling a bit more and there seem to be high frequency inverters as well. They should have lower power draws, but it is sometime to look at. Sterling seems more in Uk and Australian markets. I would assume by your user name your in Australia. Maybe someone else can recommend a decent inverter that is easily accesible to your location.
Matthew
Hi Matthew, despite my name im actually in England UK, (south east)
• Registered Users Posts: 10
Re: 24v wiring
BB. wrote: »
It all comes down to your loads--In general, a balanced off grid system design would have about 2 days of battery storage and 50% maximum discharge--Or about 4x your daily battery loads.

A wild card (for me) is the 12 volt heating pump... Is that a simple water circulation pump and a "boiler" or a refrigeration "heat pump" (i.e., reversible air conditioner--In the US we call those a "Heat Pump"). If you have A/C and/or Heat Pump, that can be a whole lot of energy usage.

What you listed is not much energy usage... Maybe something like 3.3 kWH per day (wild guess). A 24 volt battery bank would be:
• 3,300 Watt*Hours * 1/0.85 inverter efficiency * 2 days of storage * 1/0.50 max discharge * 1/24 volt battery bank = 647 Amp*Hour @ 24 volt battery bank

So, your present battery bank is:
• 6 volts * 100 AH * 28 Batteries * 1/7 parallel strings = 700 AH @ 24 volts (with 4x 6 volt batteries in series x 7 strings).

So--Roughly, your present battery bank is about the right size--But your choice of batteries should be different (in my humble opinion). For example, at a minimum, use 6 volt @ 220 AH batteries. 4 batteries in series in 3 parallel strings would give you ~660 Amp*Hour @ 24 volts. Even larger batteries to get down to one or two parallel strings would be better.

You can go with even larger batteries--Such as Fork Lift -- But those batteries are on the order of 1/2 a ton (~600 kg). I guess that you will be moving the batteries around by hand, so you need to keep the batteries small enough for one or two people to move around. You could build a single string of 4 series (4 volt battery @ 683 AH each) 123 kg cells.

Charging wise from solar, we do two calculations--One sizing the panels for the battery bank, and second based on how much power you use and how sunny your area is... For example based on 5% to 13% rule of thumb charging:
• 660 AH * 29 volt charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,243 Watt array minimum
• 660 AH * 29 volt charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,486 Watt array nominal
• 660 AH * 29 volt charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,231 Watt array "cost effective maximum"

And based on hours of sun per day--In much of of the US, we can get 4 hours or more of "full noon time sun per day" for 9+ months of the year... Using PV Watts and London UK, fixed array tilted to latitude:
```Month    Solar Radiation (kWh/m2/day)
1      1.45
2      1.90
3      2.55
4      3.99
5      4.60
6      4.38
7      4.63
8      4.52
9      3.56
10      2.64
11      1.61
12      0.97
Year      3.07
```

2.55 hours of sun per day for 8 months a year:
• 3,300 Watt*Hour per day * 1/0.52 system eff * 1/2.55 hours of sun per day = 2,489 Watt array "break even" February

You have to pick the size of array based on how much room you have, and how much you can justify.

Regarding the genset--That is a very large generator for this size battery bank/set of loads... For the battery bank, a good sized rate of charge would be 5-13% (same as solar), but we can pick two numbers: 10% for "gentle" charging (most efficient both for battery life and fuel usage on genset) and 20% (25% maximum recommended) for reducing generator run-time (smoke and noise):
• 660 AH * 29 volts charging * 1/0.80 charger eff * 1/0.67 Power Factor * 0.10 rate of charge = 3,571 VA AC generator load "nominal"
• 660 AH * 29 volts charging * 1/0.80 charger eff * 1/0.67 Power Factor * 0.20 rate of charge = 7,142 VA AC generator load "bit over-sized battery charger" (watch battery bank temperature during charging)

For diesel gensets, generally you would want to run that at 40-60% minimum load for generator life (prevent wet stacking, carbon build up, cylinder wall glazing, etc.).

Of course, my calculations are all based on a guess of 3.3 kWH per day or, roughly:
• 3,300 WH * 0.85 inverter eff * 1/12 volt battery bank = 234 AH @ 12 volts per day

If your only loads are for the battery bank, you can use a much smaller genset and save a lot of fuel costs (probably 1/2 to 1/4 the fuel usage over your 48 kW genset)--Unless you use the genset for other loads (cooking, ship's loads, etc.).

Anyway--A quick back of the envelope calculation.

Can you give us a better estimate of power usage? 3.3 kWH per day is what I use for a small, energy efficient, off grid home with a full size (energy efficient) refrigerator, lights, laptop computer/TV/Cell Charger, water pump, washing machine type loads... Energy usage is a highly personal set of choices... What works for one person may not for another.

-Bill

Hi Bill
Ive worked out my consumption at between 3.2-3.5 kWh per day,
I have a 30amp @12v battery charger running from my generator, but thinking of replacing it with a large alternator 160amps?
so at the moment, its not efficient use of the generators power.
I do use the genset for other stuff, welding, power tools, ships plant etc,

Thanks for the equations, 2489 watt array is much more than I imagined i would need, I do intend to add more panels as money allows looks like ill be needing 6 more.
hence might be a good idea to go to 48v to allow me to increase array, without having to spend on another controller (money is very limited)

so, i think your saying that i should go 24v using 660Ah bank, is this correct?

sorry if im being a bit stupid, i very new to all this and its frying my Brain
• Registered Users Posts: 10
Re: 24v wiring
Welcome to the forum "Ozparker"!

Thanks Wayne
Couple of things - - first, your panels - - "235 watts @ 38 amps" - - I'm assuming you meant to say 235 watts @ 38 volts.
Most important is your batteries - - - Twenty eight batteries of 6 volts each. That many batteries are going to be trouble.
To get 24 volts, connect 4 of these 6 volt batteries in series. Then id you intend to use all of them, which I assume you are, you'll have to make 7 identical strings of 4 batteries, then connect the 7 strings in parallel. That's where the trouble will start. It will be virtually impossible to balance out the charging and discharging of all those strings so that all the batteries are charged and discharged equally, together, all the time. And this will create real problems for your batteries. In fact, 3 strings are the max recommended, because of this problem.

If I only used 24 batteries, in 6 strings of 4 @ 24v, connected in parallel, is there a way to connect them to charge and discharge equally?
Regards Oz
• Solar Expert Posts: 3,738 ✭✭✭✭
Re: 24v wiring
Ozparker wrote: »
If I only used 24 batteries, in 6 strings of 4 @ 24v, connected in parallel, is there a way to connect them to charge and discharge equally?

There is no way Here's a short thread that explains why. --vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Banned Posts: 17,615 ✭✭
Re: 24v wiring

The more strings and/or lower system Voltage the greater the potential for current sharing problems between strings.

I wouldn't go more than two in parallel on a 12 Volt system, three on 24 Volts, and four on 48.

This does not mean six parallel strings will not work nor that it will absolutely have problems or even if it does that the problems will be so severe as to be debilitating to the system. It's just tempting providence.
• Registered Users Posts: 10
Re: 24v wiring
The more strings and/or lower system Voltage the greater the potential for current sharing problems between strings.

I wouldn't go more than two in parallel on a 12 Volt system, three on 24 Volts, and four on 48.

This does not mean six parallel strings will not work nor that it will absolutely have problems or even if it does that the problems will be so severe as to be debilitating to the system. It's just tempting providence.

Thanks for the advice Cariboocoot

so given the system if have so far,,,

24 x 6v @100 ah batteries
morningstar mppt 45 amp
235 watt, 38 amp panels x 4

and daily power usage of 3.4 kWh

would you recomend either 48v system, 3 strings of 8 batteries
or 24v system, I could seperate into 2 banks, 3 strings of 4 batteries with a changeover switch?

also I would like to add more input to the system when i have more cash, either more pv or maybe water turbine (i live on a fast flowing river)
• Banned Posts: 17,615 ✭✭
Re: 24v wiring

Your first problem is that you will not get 3.4 kW hours of power out of 940 Watts of panel. As such you either have to shrink the loads, increase the panels, or run the generator.

To get 3.4 kW hours AC from batteries you need an allowance for conversion efficiency and powering the inverter. This would be about 10% more for conversion and perhaps 480 Watt hours for the inverter or about 4.2 kW hours DC.

Now divide that by either of the nominal Voltages and what do you get? About 200 Amp hours on 24 Volts, 100 on 48. That sort of looks like 48 Volts would be the better choice here (four parallel 100 Amp hour strings giving the power requirement @ 25% DOD).

At that battery size you should have about (40 Amps * 48 Volts / 0.77 efficiency) about 2.5 kW array.

So ... how do you want to go with this?
• Super Moderators, Administrators Posts: 30,485 admin
Re: 24v wiring
Ozparker wrote: »
Hi Bill
Ive worked out my consumption at between 3.2-3.5 kWh per day,
I have a 30amp @12v battery charger running from my generator, but thinking of replacing it with a large alternator 160amps?
so at the moment, its not efficient use of the generators power.
I do use the genset for other stuff, welding, power tools, ships plant etc,

Thanks for the equations, 2489 watt array is much more than I imagined i would need, I do intend to add more panels as money allows looks like ill be needing 6 more.
hence might be a good idea to go to 48v to allow me to increase array, without having to spend on another controller (money is very limited)

so, i think your saying that i should go 24v using 660Ah bank, is this correct?

sorry if im being a bit stupid, i very new to all this and its frying my Brain

There are a lot of things to "balance"... You can take the equations and put them in a spread sheet (if you wish). Makes playing with the numbers a bit easier.

If you try for the ~10% rate of charge--Basically a 660 AH battery bank (any voltage) would be around 66 amps of charging current (or 120 Amps if you want 20% rate of charge)...

For the most part, I try to suggest people stay around 100 Amps maximum--Or you start looking at really heavy (and expensive) copper wiring. And Solar charge controllers tend to top out around 60-80+ amps maximum (12/24/48 volt banks). So, if you need to add more current than 60-80 amps, you need a second charge controller--That is one reason why going to the next larger bank voltage makes sense--2x the voltage means 1/2 the charging current.

The higher end (and newer) charge controllers will work at 12-48 volts--They don't care. Just respect the maximum output current (MPPT charge controllers usually, not always, have the ability to control their maximum output current by "clipping" the input power... PWM controllers need to limit the size of the solar array).

Battery wise--100 AH at 12 volts are not very big guys. You may be "stuck" with what you have until you get your money's worth out of them.

In the US, 6 volt @ ~220 AH "golf cart" batteries tend to be cheap and relatively rugged (get 3-5+ years from them). And if you spend 2x, you may get 6-8+ years.

I don't want to see you get "wrapped up" in battery bank specific just yet. If you are satisfied with the recommendations for a ~3.3 kWH per day load (2 days, 50% max discharge for longer battery life)--Then any configuration of bank (1,320 AH @ 12 volts; 660 AH @ 24 volts; 330 AH @ 48 volt) will work OK in that all these banks store the same amount of kWH worth of energy.

It is the "other electrical issues" (charging current, max load current, etc.) and even simple things like -- How big of battery can you move around on the boat (i.e., a bunch of 120 kg cells or one 1,000 kg battery) and what is available at a reasonable price should all be taken into account.

Regarding current... A 100 amp nominal current at 12 volts will give you a 1,200 watt output. But the "deratings" make things a lot "worse" (more expensive). That 1,200 watt @ 12 volt inverter needs, wiring/fuse/breaker wise:
• 1,200 watts * 1/0.85 inverter eff * 1/10.5 inverter cutoff * 1.25 NEC derating (breaker/wiring) = 168 Amp minimum branch circuit (if using typical home type building codes)

Regarding AC (or DC) generator design... Lookng for fuel efficiency. Just like you cannot expect a small motor cycle to pull a double trailer... You would not take a Highway Tractor to the local store.

Size the charging source to the battery bank... And not all charging sources are capable of supplying 100% rated output to a large battery bank for multiple hours (i.e., a typical automotive alternator will overheat if you attempt to run it at maximum output for several hours). And many have internal voltage regulators that you cannot adjust.

You can look at trucking/marine alternators (such as Balmar) for ones that would be better to strap onto a motor.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 3,738 ✭✭✭✭
Re: 24v wiring
Ozparker wrote: »
would you recomend either 48v system, 3 strings of 8 batteries
or 24v system, I could seperate into 2 banks, 3 strings of 4 batteries with a changeover switch?

Do not make the decision to go 24 or 48 based on the batteries you have now. Make the decision based on your ultimate needs. Your current batteries are temporary.

Several folks here have used two battery banks with a selector switch. There are a few issues to work around, but depending on your needs it may be a workable system. Battery selector switches come in two flavors:
1) make-before-break....when switching from one bank to the other, both batteries are connected for a moment. The problem is that the charged bank will want to discharge into the discharged bank during that moment. This is tough on the switch.
2) break-before-make....one bank is disconnected before the other is connected. The problem is that you must shut down your inverter and charge controller before making the switch. Neither the inverter or the controller will be happy to have their battery disconnected and reconnected while they are functioning.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Registered Users Posts: 10
Re: 24v wiring
BB. wrote: »
There are a lot of things to "balance"... You can take the equations and put them in a spread sheet (if you wish). Makes playing with the numbers a bit easier.

If you try for the ~10% rate of charge--Basically a 660 AH battery bank (any voltage) would be around 66 amps of charging current (or 120 Amps if you want 20% rate of charge)...

For the most part, I try to suggest people stay around 100 Amps maximum--Or you start looking at really heavy (and expensive) copper wiring. And Solar charge controllers tend to top out around 60-80+ amps maximum (12/24/48 volt banks). So, if you need to add more current than 60-80 amps, you need a second charge controller--That is one reason why going to the next larger bank voltage makes sense--2x the voltage means 1/2 the charging current.

In the US, 6 volt @ ~220 AH "golf cart" batteries tend to be cheap and relatively rugged (get 3-5+ years from them). And if you spend 2x, you may get 6-8+ years.

My friend has the same batteries as me (yuasa endurance SLA 6v 100ah) his bank is currently 9 years old and still very good, so im hoping:-) that I might expect the same, "if" correctly used and connected.
Which is why I'm so concerned about setting it all up correctly, how many strings @ what voltage etc?

i have decided to change my lighting, laptop chargers and tv to 12v, so only needing to use inverter occasionally, Ive worked out that this should bring my consumption down to 2.4 kWh per day

given that my consumption is now 2.4 kWh, and that the inverter would only be for occasional use (I use the Genset for high consumption items)
Should that make a difference wether I go 24v or 48v?

Regarding AC (or DC) generator design... Lookng for fuel efficiency. Just like you cannot expect a small motor cycle to pull a double trailer... You would not take a Highway Tractor to the local store.

As far as the Genset, I have a large (28kw) 3 phase, this is used to air-start the ships engine, Also welding, and most wastefully when my girlfriend Dries and Straightens her hair:grr

Size the charging source to the battery bank... And not all charging sources are capable of supplying 100% rated output to a large battery bank for multiple hours (i.e., a typical automotive alternator will overheat if you attempt to run it at maximum output for several hours). And many have internal voltage regulators that you cannot adjust.

Next year Im going to set up small battery charging genset, single cylinder diesel with good alternator (possibly Balmar)
• Super Moderators, Administrators Posts: 30,485 admin
Re: 24v wiring

9+ years from a SLA is doing really well. Figure out what your friend is doing (loads/charging/hours of charging/etc.) is doing and copy that.

If the battery bank is close to the loads--12 volts can work. Many "12 volt" devices do not like the wide voltage swings you can see on a deep cycle battery bank (from 10.5 to 15+ volts)... With SLA batteries, you normally are limited to about 14.2 to 14.4 volts maximum--And on a ship, they will probably not see sub freezing temperatures (cold batteries need higher charging voltages).

I still like suggesting AC inverter for your loads rather than sticking with 12 VDC--One of the issues is that it limits you to 12 VDC "forever"--Making it very difficult to raise your battery bank voltage to 24 or 48 volts (if you install a 24 to 12 volt converter--That is pretty close to the losses of an AC inverter anyway).

You can find 24 VDC appliances (trucking/marine stores), but that usually is more costly and still limits you to specialized appliances.

Regarding what AC inverter--It is back to loads. If you have smaller loads, a small TSW (true sine wave inverter) can be efficient and will allow you to use standard 120/230 VAC loads--And allow you to wire up AC outlets around the ship beyond the 12 volt power nexus.

If you have large loads (hair dryer), then that either drives up the size of the AC inverter--Or you get two inverters--the small/low power/high quality TSW AC inverter--And a second "cheap" MSW inverter that you only turn on when you need the higher current (or a second large capacity TSW inverter if you are made of money). Having a small always one AC inverter can make it pretty nice for everyone aboard.

Another thing to look at is the AC inverter options... You can get (more expensive) inverters that have "search mode" where the inverter uses much less power (it turns on once a second for a few cycles looking for >6 watts of loads, if load is found, it turns on 100% of time until loads go away). And there is also a remote on/off input. Allows you to manually (or through some control automatically) when AC power is needed.

If you stick with 12 VDC power, the MorningStar 300 Watt TSW 12 VDC inverter is a really nice unit--I have not seen any other small inverters with the search/remote on-off options.

If you go larger, Victron (I believe) and Samulex (and others I am sure) make some good quality smaller AC inverters with interesting options (remote panels, etc.). Otherwise, you are looking at larger/more expensive inverters for 24/48 volt battery banks. And at 48 volts, it is very difficult to find "small" AC inverters--They are, for the most park, several kWatt or larger units (and 20-40+ watts of losses just "turned on").

Do not get stuck in looking for inverters until you got your loads nailed down.

Back to your battery bank--I suggest getting an AC/DC Current Clamp DMM meter (in the US, Sears has a "good enough" meter that is pretty nice for the price).

Just monitor the voltage across the batteries and the current through each string during heavy charging/loads--Making sure that each parallel string carries its share of the current. Anything that is "different" needs to be checked.

Wiring parallel batteries this way is highly suggested.

And, consider placing a fuse per battery string to protect against short circuits. These BlueSea fuse holders are pretty nice for the job (not cheap when you add the fuses):

http://www.bluesea.com/products/category/Fuse_Blocks/Terminal_Fuse_Blocks

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 10
Re: 24v wiring

If the battery bank is close to the loads--12 volts can work. Many "12 volt" devices do not like the wide voltage swings you can see on a deep cycle battery bank (from 10.5 to 15+ volts)... With SLA batteries, you normally are limited to about 14.2 to 14.4 volts maximum--And on a ship, they will probably not see sub freezing temperatures (cold batteries need higher charging voltages).

Thats a good point, some of the ships gear (Depth finder) does struggle with the varied voltages.

I currently have a 12v/240v AC inverter 2.7kw, running from my 12v bank, which until now have been charging with my Genset. this has become too expensive both in diesel and wear & tear,
so,,,, I decided to buy some panels,
Problem is that I bought my panels knowing "nothing" about this subject.
I assumed all panels would be fine in a 12v system

the panels i bought are, 235 watt, 38v, sharp x4, I then bought a morning star 45amp MPPT

I still like suggesting AC inverter for your loads rather than sticking with 12 VDC--One of the issues is that it limits you to 12 VDC "forever"--Making it very difficult to raise your battery bank voltage to 24 or 48 volts (if you install a 24 to 12 volt converter--That is pretty close to the losses of an AC inverter anyway).

I like the idea of running everything through an AC inverter as it keeps things more simple and use-friendly for my GF (and me)
My lighting runs through the inverter (240v) i was thinking of changing it to a 12v circuit running directly from the Batteries? so, what your saying is, if I go 24v or 48 volt, I will still make losses by running it through a 24-12v converter , so maybe I should keep it at 240v through the inverter?
i assume the same applies to lap-top chargers etc?

Regarding what AC inverter--It is back to loads. If you have smaller loads, a small TSW (true sine wave inverter) can be efficient and will allow you to use standard 120/230 VAC loads--And allow you to wire up AC outlets around the ship beyond the 12 volt power nexus.

If you have large loads (hair dryer), then that either drives up the size of the AC inverter--Or you get two inverters--the small/low power/high quality TSW AC inverter--And a second "cheap" MSW inverter that you only turn on when you need the higher current (or a second large capacity TSW inverter if you are made of money). Having a small always one AC inverter can make it pretty nice for everyone aboard.

funds are limited at the moment, but we could afford a small sine wave inverter, then at a later date, get a second larger one.
Also we time running large loads for when the Genset, is running (hairdryers etc), so at the moment we are only looking at running small loads, but for several hours, (short winter days)

Another thing to look at is the AC inverter options... You can get (more expensive) inverters that have "search mode" where the inverter uses much less power (it turns on once a second for a few cycles looking for >6 watts of loads, if load is found, it turns on 100% of time until loads go away). And there is also a remote on/off input. Allows you to manually (or through some control automatically) when AC power is needed.

If you stick with 12 VDC power, the MorningStar 300 Watt TSW 12 VDC inverter is a really nice unit--I have not seen any other small inverters with the search/remote on-off options.

Do not get stuck in looking for inverters until you got your loads nailed down.

Im going to work out my loads tonight!

Im definitely getting the feeling that a 24v system is the way to go, considering the points you have made, ease of wiring, availability of components and appliances etc

Back to your battery bank--I suggest getting an AC/DC Current Clamp DMM meter (in the US, Sears has a "good enough" meter that is pretty nice for the price).

thanks for that, i will look into getting a current clamp DMM meter soon, probably the one you have suggested!

Just monitor the voltage across the batteries and the current through each string during heavy charging/loads--Making sure that each parallel string carries its share of the current. Anything that is "different" needs to be checked.

Wiring parallel batteries this way is highly suggested.

And, consider placing a fuse per battery string to protect against short circuits. These BlueSea fuse holders are pretty nice for the job (not cheap when you add the fuses):

http://www.bluesea.com/products/category/Fuse_Blocks/Terminal_Fuse_Blocks

will do

Regards Oz

-Bill[/QUOTE]
• Super Moderators, Administrators Posts: 30,485 admin
Re: 24v wiring
Ozparker wrote: »
I currently have a 12v/240v AC inverter 2.7kw, running from my 12v bank, which until now have been charging with my Genset. this has become too expensive both in diesel and wear & tear,
so,,,, I decided to buy some panels,
Problem is that I bought my panels knowing "nothing" about this subject.
I assumed all panels would be fine in a 12v system

the panels i bought are, 235 watt, 38v, sharp x4, I then bought a morning star 45amp MPPT

Generally, a good MPPT controller (like the MorningStar TS MPPT line) will work fine... There can be an issue with some solar panel Vmp voltages and 48 volt battery banks where you cannot use ~50-70 volt Vmp panels on many MPPT controllers and 48 volt battery banks (one panel is too low of Vmp and two panels in series is too high of Voc-cold ratings for the controller)--Does not happen often, but it can.
I like the idea of running everything through an AC inverter as it keeps things more simple and use-friendly for my GF (and me)
My lighting runs through the inverter (240v) i was thinking of changing it to a 12v circuit running directly from the Batteries? so, what your saying is, if I go 24v or 48 volt, I will still make losses by running it through a 24-12v converter , so maybe I should keep it at 240v through the inverter?
i assume the same applies to lap-top chargers etc?

It can be close--Converters are converters whether DC to DC or DC to AC... You have to look at the specifications to be sure (and not all specifications are clear on converter losses).

I would suggest getting a Kill-a-Watt type meter so you can measure your AC loads--It will make things much more clear and less guesswork.

http://www.amazon.co.uk/tag/kill-a-watt/products

Regarding what AC inverter--It is back to loads. If you have smaller loads, a small TSW (true sine wave inverter) can be efficient and will allow you to use standard 120/230 VAC loads--And allow you to wire up AC outlets around the ship beyond the 12 volt power nexus.
funds are limited at the moment, but we could afford a small sine wave inverter, then at a later date, get a second larger one.
Also we time running large loads for when the Genset, is running (hairdryers etc), so at the moment we are only looking at running small loads, but for several hours, (short winter days)

Yep--But excluding heating/large tools, smaller AC inverters will supply many smaller loads (and CFL/LED lighting). Conservation is your friend here (usually cheaper to conserve than to generate power).
Im going to work out my loads tonight!

Im definitely getting the feeling that a 24v system is the way to go, considering the points you have made, ease of wiring, availability of components and appliances etc

Back to your battery bank--I suggest getting an AC/DC Current Clamp DMM meter (in the US, Sears has a "good enough" meter that is pretty nice for the price).

Yep, loads define the battery bank, then loads and battery bank define the charging requirements.
thanks for that, i will look into getting a current clamp DMM meter soon, probably the one you have suggested!

The way this meter "zeros" DC current readings is a bit strange... Once you understand it--It is fine. Ask here if you have questions.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset